This revised proposal seeks continued support for an interdisciplinary, predoctoral training program centered in bioorganic and bioinorganic chemistry. Support is requested initially for 12 graduate trainee positions, and increasing to 15. Thirteen faculty from the Divisions of Biology and Chemistry and Chemical Engineering will participate in training predoctoral students. The aim of the proposed program is the training of students in the chemical design, synthesis, elucidation, and functional application of organic and metal-containing molecules of biological importance. With this emphasis on interdisciplinary research, students will be trained to apply a chemical perspective, grounded in considerations of structure and mechanism, to explore biological function. Through chemical synthesis and design, trainees will become able to probe, modify, and create biological function. In this revision we seek to emphasize training across the disciplines, in particular to encourage our students to develop an understanding of where chemical tools and principles can be powerfully applied in biological systems. Facilities will include the research and teaching facilities of both Divisions at Caltech as well as the Beckman Institute, where chemists and biologists conduct research in shared laboratory resource centers. The course curriculum will provide students with a foundation in both chemistry and biology, but strong emphasis will be placed on training in the context of the research experience. The potential pool of students for the program already at Caltech is estimated as greater than 70 students, all of outstanding quality and talent, and with excitement for conducting research at the interface of chemistry and biology. We propose this training program in bioorganic and bioorganic chemistry, using chemical design to explore biological function, to become a focal point at Caltech, where students are trained for leadership roles in both academic and industrial research at the interface of chemistry and biology.